Drop support for Python 3.8 (and maybe 3.9)

[antazoey]

Overview

Vyper itself requires 3.10 these days.
Python 3.8 is no longer supported, not even security updates.

[charles-cooper]

i think vvm should be even more stable than vyper - we want to maximize the probability that you can run it from an old machine and it still works. there isn't really any harm to supporting older versions of python, as long as there is no maintenance burden i don't think we need to explicitly drop support for older python versions.

[antazoey]

That is fair, but unless every older version of Python persists in the testing matrix, there is no guarantee. Plus, you can always simply use older versions of vvm.